Tuned magnetron



y 1956 E. c. OKRESS 2,748,314

TUNED MAGNEIRON Filed July 15, 1954 wl'rmzssss'. iNVENTOR Ernest C.OKress.

United States Patent '0 TUNED MAGNETRON Ernest C. Okress, Elmira, N. Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 15, 1954, Serial No. 443,589

12 Claims. (Cl. 315-3959) My invention relates to magnetrons and in particular to an improved arrangement of annular rings or straps which interconnect alternate poles of the magnetron with each other and thereby give greater stability to the frequency of oscillation, known as the 1r-mode, at which it is desired that the magnetron shall operate.

During the last decade or so, magnetron oscillation generators of the general form shown in Fig. 1 herein, having a central cathode surrounded by an annular anode containing a number of radially-extending resonating cavities have come into wide use for generating ultra-high frequency oscillations. The portions between adjacent cavities on the inner face of the annular anode are known as segments, and this entire anode structure constitutes a system comprising a plurality of. electrical resonators which are capable of sustaining a number of different modes of oscillation. The most stable and etficient mode, and the one desired in almost all practical cases today, is that known as the vr-mode, in which adjacent poles are of opposite polarity, (e. g., It has been found that the tendency of the magnetron to maintain the 1r-mode of oscillation is increased if the annular rings commonly known in the art as straps are-provided which tie together alternate segments, the joints being as direct and of as low impedance as possible.

An improvement in performance results if the length of straps between alternate segments is made as short as possible with respect to the wavelength of the 1r-mode. With high power magnetrons, the larger anode size requires longer length of straps between alternate segments. This reduces mode separation with respect to the adjacent competing mode and reduces stability of the 1r-mode and therefore any way to avoid these would improve the performance of the magnetron. The present invention presents one solution to this problem by electrically reducing the inductive reactance of the straps between adjacent cavities. This is done by terminating the straps in lengths of coaxial line which adds the desired reactance to reduce the impedance of the strap. Thereby tighter coupling between cavities of like polarity is achieved and the stability of the desired 1r-rnode of oscillation of the magnetron is increased.

One object of my invention is, accordingly, to provide an improved magnetron oscillation generator.

Another object is to provide an improved system for improving the stability of 1r-rnode of oscillation in a symmetric strapped magnetron oscillator.

Another object is to provide a structure for magnetron oscillators of high power and high frequency stability.

Another object is to provide a structure for increasing the stability of magnetron oscillators of large size for high power applications.

Another object is to provide an improved structure for maintaining the 1r-mode of operation in magnatrons.

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawings, in which:

Figure 1 is a view in section showing the general structure of magnetron embodying one species of my invention;

Fig. 2 is an enlarged view along the section II-II in Fig. l; and

Fig. 3 is a view similar to Fig. 2 of a modified form of my invention.

Referring in detail to Fig. 1, the magnetron has a cylindrical casing 1 supporting an annular anode 2, both of which may be of copper. Central within the anode is an electron emissive cathode 3 of a type well known in the art. Eight cylindrical chambers 4, uniformly spaced, are formed in the anode structure, each being connected with the inner face of anode annulus by a radial throat 5. The remaining portions 6 of the anode extending between the chambers 5 are the segments mentioned above, and in the Ir-mode of oscillation of the magnetron adjacent segments 6 are respectively positive and negative in electrical potential at any instant. A unidirectional magnetic field perpendicular to the plane of Fig. 1 is impressed by magnetic means, not shown.

As is shown more clearly in Fig. 2, a channel or strap groove 7 is cut in the upper face of the segments 6, and an annular ring or conducting loop 8 frequently called a strap, which is usually of copper, is supported in uniformly spaced relation in the strap groove 7. In accordance with my present invention, the strap 8 is supported by rod 9 in cylindrical hole 10 and terminated to the anode structure to form coaxial supporting lines. The lengths of all coaxial supporting lines is adjusted so that the inductive reactance of the strap 8 between terminations 11 are reduced to a negligible value. All segments having a common electrical polarity in the 1r-mode of oscillation of the magnetron are thus connected together by an electrical path of low impedance.

In the magnetron of Figs. 1 and 2, a second channel 7' and strap 8' (not shown) would be provided in the lower face of the segments 6, and this strap would tie together the segments 6 which were not interconnected by strap 8.

The above-described modification of prior art magnetron structure produces a greater stability of oscillation in the 1r-mode. The effect of the shorted coaxial line section 9, 10 depends in ways Well known in the electrical art on its longitudinal dimensions and so may be calculated and cold-test checked for any given structure.

Figure 3 shows a modification of my invention in which the posts 9 have their ends set in the bottom of cylindrical wells 10' bored normal to the bottom of channel 7 at the midpoint of each alternate magnetron pole. A similar channel strap, post and well are formed at the other lateral face of the anode to interconnect the other set of segments.

I have described a structure for, in effect, inserting the desired neutralizing reactance in the straps so as to neutralize its inductive reactance, between alternate segments to which it is terminated. My structure is compact and well adapted to ease of manufacture. Other arrangements for introducing neutralizing reactance into this strap between alternate segments to which they are attached besides those shown may be made, and it is to be understood that these modifications thereto may be made without departing from the spirit and scope of the appended claims.

The reduction of the strap impedance which my structure effects, results in tighter coupling and inherently better mode separation and 1r-mode stability than is possible with conventional straps.

I claim as my invention:

1. A magnetron comprising a central cathode surrounded by an anode which comprises a plurality of segments projecting inward toward said cathode and separated by resonating cavities, an annular conductor surrounding said cathode and disposed adjacent said segments, said conductor being outside the direct path between said segments and said cathode, and means having a coaxial line structure connecting alternate segments to said annular conductor.

2. The structure described in claim 1, in which a second annular conductor is connected to the remaining segments by means having a coaxial line structure.

3. A magnetron comprising a central cathode surrounded by an anode which comprises a plurality of seg ments projecting inward toward said cathode and separated by resonating cavities, a conducting loop surrounding said cathode and disposed adjacent said segments, said conducting loop being outside the direct path of electron flow between said segments and said cathode, and means having a coaxial line structure connecting alternate segments to said conducting loop.

4. The structure described in claim 3, in which a second conducting loop is connected to the remaining segments by means having a coaxial line structure.

5. A magnetron comprising a central cathode surrounded by an anode which comprises a plurality of segments projecting inward toward said cathode and separated by resonating cavities, an annular conductor surrounding said cathode and disposed adjacent said segments, said conductor being outside the direct path between said segments and said cathode, and a connection between every alternate segment and said annular conductor comprising a conductor extending into a hole formed in said anode.

6. The structure described in claim 5, in which a second annular conductor is connected to each of the remaining segments by a conductor extending into a hole formed in said anode.

7. A magnetron comprising a central cathode surrounded by an anode which comprises a plurality of segments projecting inward toward said cathode and separated by resonating cavities, an annular conductor surrounding said cathode and disposed adjacent said segments, said conductor being outside the direct path between said segments and said cathode, and a connection between every alternate segment and said annular conductor comprising a conductor extending along the axis of a cylindrical well formed in said anode.

8. The structure described in claim 7, in which a second annular conductor is connected to each of the remaining segments by a conductor extending along the axis of a cylindrical hole formed in said anode.

9. A magnetron comprising a central cathode surrounded by an anode which comprises a plurality of segments projecting inward toward said cathode and separated by resonating cavities, a conducting loop surrounding said cathode and disposed adjacent said segments, said conducting loop being outside the direct path of electron flow between said segments and said cathode, and a connection between every alternate segment and said conductive loop comprising a conductor extending into a hole formed in said anode.

10. The structure described in claim 9, in which a second conducting loop is connected to each of the remaining segments by a conductor extending into a hole formed in said anode.

11. A magnetron comprising a central cathode surrounded by an anode which comprises a plurality of segments projecting inward toward said cathode and separated by resonating cavities, a conducting loop surrounding said cathode and disposed adjacent said segments, said conducting loop being outside the direct path of electron flow between said segments and said cathode, and a connection between every alternate segment and said conductive loop comprising a conductor extending along the axis of a cylindrical well formed in said anode.

12. The structure described in claim 11, in which a second conducting loop is connected to each of the remaining segments by a conductor extending along the axis of a well formed in said anode.

References Cited in the file of this patent UNITED STATES PATENTS 

